298 WALKS AND TALKS. 



cats only in the same way as the latter differ among them- 

 selves. The ground for asserting that the panther, the leopard, 

 the tiger, the ocelot are descended from some common ancestry is 

 precisely the same as for maintaining, among domestic cats the 

 common ancestry of the brindled Tabby, the tortoise-shell 

 Spanish, the slaty Chartreuse, the short-tailed Malayan, and 

 the tailless Manx. The analogies compel us to admit that all 

 the members of the cat-family are related by blood. We must 

 say the same of the dog-family, and of the other families 

 which include the horse, the ox, the sheep, the squirrel, and 

 also, the families of the lower classes, Birds, Reptiles, and 

 Fishes. 



But it is impossible to stop here. The Lynx family and 

 the Cat family do not differ more than Africans and Europeans ; 

 there is the same reason for recognizing in them a common 

 descent. So of the dog-family and the hyaena-family. So of 

 the perch and sun-fish families. So of all families. And now 

 to make the matter short, for lack of space, I venture to state 

 in general, that in the structural affinities of all animals 

 certainly those of the same sub-kingdom we have relation- 

 ships which justify the inference of common genealogical de- 

 scent. The differences have arisen partly from differences in 

 situation and a tendency in the organism to vary in the direc- 

 tion of better adaptation to the environment. 



What next, of the succession of animals in geologic time ? 

 I think you are ready to admit that the succession is a real 

 progress. I think you will admit in several instances, the 

 graduation from lower to higher is shown to proceed by very 

 short steps. Consider especially, the horse-series, and the two 

 series reaching from reptiles to birds (stru'thious and eurinatc) 

 (Talk XLV). Remember that these are only instances out 

 of many which are similar in meaning, though less striking 

 in completeness. Consider the probability that if the record 

 of extinct life were fully restored, we should recognize the 

 entire succession as a nicely graduated series, with numerous 

 diverging branches also nicely graduated the whole reaching 

 from some primeval type through many ramifications, to the 



